1. Field of the Invention
The present invention relates to a zoom lens system. More specifically, though not exclusively, the invention relates to a zoom lens system that can be used as an image pick-up optical system in an image pick-up apparatus.
2. Description of the Related Art
If vibration is generated in the image pick-up system when capturing an image of an object, the captured image can be blurry. To prevent such blurring of the captured image, various known vibration control optical systems have been discussed.
Many known zoom lens systems, functioning as photographic systems, compensate for blurring of an image by displacing some lens groups.
There is a known zoom lens system including four groups of lenses, i.e., a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power, disposed in order from the object side to the image side of the lens system. This zoom lens system facilitates obtaining a still image by vibrating the entire third lens group in a direction orthogonal to the optical axis (refer to Japanese Patent Laid-Open No. 10-260356).
The assignee of the present invention has proposed a four-group zoom lens system having a vibration control function. The lens groups of the zoom lens system includes a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power. An aperture stop is provided between the second lens group and the third lens group. The third lens group is divided into a negative lens sub-group having negative refractive power and a positive lens sub-group having positive refractive power. The positive lens sub-group is vibrated in a direction orthogonal to the optical axis to obtain a still image (for example, refer to Japanese Patent Laid-Open Nos. 7-128619, 11-237550, and 2002-244037).
The assignee has also proposed a zoom lens system, which can have the same structure as that of the above-described four-group zoom lens system, except that the third lens group is divided into two positive lens sub-groups having positive refractive power and one of the positive lens sub-groups is vibrated in a direction orthogonal to the optical axis to obtain a still image (for example, refer to Japanese Patent Laid-Open No. 2001-66500).
In general, an image pick-up system in which vibration is controlled by decentering some lens groups in a direction orthogonal and parallel to the optical axis is useful because a special additional optical system for controlling vibration is not required.
However, there are problems in that space for moving the lens groups is required within the optical path and that eccentric aberration can be generated while controlling vibration.
Recently, some commercially available cameras have employed a three charge coupled device (3CCD) system to improve the quality of a captured image.
There is a strong desire for a zoom lens system supporting a 3CCD system to have a high zoom ratio and a vibration control function for controlling the blurring of a captured image caused by the vibration (tilting) of the zoom lens system.
In particular, there is a strong desire for a zoom lens system, which can have a small optical system including a highly sensitive eccentric lens group, which is the lens group placed to control vibration.
However, in an optical system that controls vibration by decentering a lens group in a direction orthogonal to the optical axis, an increase the vibration control sensitivity and an increase in the zoom ratio cause an increase in eccentric aberration and a decrease in optical performance.
In particular, it can be difficult to compensate for the aberration that is generated while a lens unit is decentered at the telephoto side.
Therefore, it can be useful for a zoom lens system, which can have a vibration control mechanism, to have an optical performance that is not degraded while blurring is corrected or error reduced and with suitable vibration control sensitivity.